Alternating current (AC) type PDP devices are widely used as a flat display. The PDP device carries out grayscale display processing for grayscale expressions by using an intra-frame time division method (subfield method). In the subfield method, a field (or frame) serving as a unit of a video image display which is displayed on a display panel (PDP) is divided into a plurality of subfields (or sub-frames) to which a weight related to brightness at the time of light-on (luminance of light-emission display) is given. Further, grayscale in a cell or a corresponding pixel in the field is expressed by the combination of a light-on and a light-off (non lighting) of the subfields (selective lighting) in the field. In the grayscale display processing, according to input display data (video signal), the display data (field and subfield data) to be outputted to the display panel (PDP) is generated by conversion in accordance with selective lighting of subfields in each cell of the field. In other words, the selective lighting of subfields indicates a corresponding relation between lighting step (referred to as s) associated with grayscale values to be displayed and a combination of light-on and light-off of each subfield in the field (referred to as subfield lighting pattern or the like). Note that, though the lighting step (s) is associated with a grayscale value, they are different from each other.
At the time of displaying a moving picture on the PDP device, lines in purple red and green are generated on the contour lines in skin color portions of person's cheeks and the like. This phenomenon is called false contour or the like and deteriorates the display quality, and therefore some measures are needed. As a cause of the false contour, an absence of a light-on subfield in the subfield lighting pattern is known. The absence of a light-on subfield mentioned here means that a light-off subfield (off state) exists in the middle of a plurality of light-on subfields (on state) at a lighting step (s). For example, when a subfield lighting pattern has a binary encoded structure, a position of a bit carry and the like also correspond to this presence of a light-off subfield.
As the measures against the false contours, the following first method is known as a method which is thought to be most effective in the conventional technology. In this first method, in the case where one field is constituted of m subfields, as a structure of a subfield lighting pattern, the number of lighting steps (s) is set to m+1, and the number of light-on subfields is increased by one every time when the lighting step (s) is increased by one. By this means, an absence of a light-on subfield which is the cause of the false contour is eliminated. FIG. 16 shows an example of subfield lighting pattern in the first method. The first method is disclosed in Japanese Patent No. 3322809 (Patent document 1) and Japanese Patent No. 3365630 (Patent document 2).